The present invention relates to an oil control valve, and more particularly, to an oil control valve for controlling operation of a camshaft in a continuously variable valve timing system.
Generally, operation of a camshaft in a continuously variable valve timing system is controlled by oil pressure, and an oil control valve regulates a supply of oil which controls the operation of the camshaft.
The oil control valve includes a housing, a spool disposed inside the housing, a return spring for elastically supporting the spool, and a magnetic coil for producing a magnetic field. The spool is activated by a magnetic force of the magnetic field. By regulating current supplied to the magnetic coil, the operation of the spool can be regulated.
Hydraulic oil that contains foreign particles circulates within the oil control valve, so the oil control valve gathers such particles, and these particles have bad effects on the operation of the oil control valve. In order to eliminate such particles that remain inside the oil control valve, an oil control valve cleaning mode is periodically performed.
During the oil control valve cleaning mode, the spool that is disposed inside the housing of the oil control valve endures full reciprocal movements so that the particles are broken into smaller particles by the collision between the spool and an end wall of the housing. The smaller particles are discharged from the housing through an opening hole formed in the housing, and they are then trapped by an oil filter.
During such a cleaning mode, the spool collides with the end wall of the housing, and therefore noise occurs. In order to reduce such noise, that is, in order to prevent the spool from colliding with the housing, it is necessary to have a minimum gap between the housing and the spool such that collision does not occur. The gap can be determined by trial and error, and the operation of the spool is regulated according to the gap. However, such a method requires a long period of time. Furthermore, because resistance of the magnetic coil varies according to temperature, intensity of the magnetic field also varies according to temperature. Thus, the operation of the spool is affected by temperature so that collision between the spool and the housing even after regulation of the operation of the spool occurs intermittently. Moreover, if the spool moves at a high speed, a resonance may occur between the spool and the return spring so that the oil control valve may be damaged by the collision between the spool and the housing.
In a preferred embodiment of the present invention, the oil control valve comprises a housing, a spool, and a damping unit. The spool is movably disposed inside the housing, and the damping unit is disposed between a distal end of the spool and an end wall of the housing such that an impact generated by a collision of the spool at the end of its travel decreases.
It is preferable that the damping unit comprises an elastic spacer and a stopper. The elastic spacer is disposed in contact with the end wall of the housing, and the stopper is disposed in contact with the spacer, the stopper being provided with an opening hole formed therethrough.